First, a terrifying case of road rage, all caught on tape. Frantic 911 call, telling the story of a driver out of control and how an innocent young woman became a victim. Abc's marci gonzalez has more on this chilling young story. We have a red pickup truck following us. Reporter: This anxiety-filled 911, came in to police in gainesville, georgia, early friday morning. He hit us. Reporter: From a couple being rammed by a pickup truck at full speed on the highway. He keeps hitting us. Reporter: According to police, the situation then turned horrific, as the caller's watched the pickup truck's driver swerve into oncoming traffic. He's about to hit somebody head-on. Reporter: Investigators say that's when 48-year-old michael williams, behind the wheel of the pickup truck, hit 22-year-old chelsea garish head-on, killing both drivers. He just hit somebody head-on. No, no, no. Ma'am? Ma'am? Calm down. He hit somebody going head-on going about 70 miles per hour. Reporter: The couple heard on the 911 call has not been identified by police, who are still working to find out why this happened. And there were two other women in the car with garish. Both were taken to the hospital and are expected to recover. But police say those people who dialed 911 did the best thing, calling for help and not pulling over.

This transcript has been automatically generated and may not be 100% accurate.

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